There are known optically anisotropic crystal films, which are obtained from polycyclic organic compounds via special fabrication operations and therefore feature high degree of anisotropy, thermal and light resistance. Technology of fabricating the above films is relatively simple; however it requires special equipment and precise compliance with the fabrication conditions in order to provide reproducibility of parameters of films. During fabrication of light, indicatory and other devices, which mainly represents assembly of already prefabricated parts, it is sometimes difficult to incorporate an additional fabrication process to produce films and parts based on the above films. Additional challenges arise when one needs to fabricate anisotropic coatings with complex configurations or with small pattern features. Usually in this case one forms a continuous anisotropic coating via the known methods and then later removes certain portions of the coating. For example, there is a known method of removing portions of the coating using scotch tape. The scotch tape is adhered to the areas of the film to be stripped of the coating, and after the tape is peeled the remaining coating on the substrate has the desired configuration. This known technique does not require special equipment, however, it does not provide sufficiently sharp edge of the coating and the degree of anisotropy at the edges of the remaining regions, and it is not reproducible enough to obtain elements of small sizes. Another difficulty is the possible decrease in the degree of crystalline order due to the application of various compressive and shear stresses to the anisotropic crystal film. Also the roughness of the surface of the anisotropic crystal film can be increased when the scotch is peeled off.
In order to fabricate polarizing coatings with the desired configuration one may also use a patterned layer of water-soluble lacquer. After solidifying the lacquer the exposed polarizing coating is washed off with a suitable solvent (water or a mixture of water with and organic solvent). However, this method also requires carrying out several additional fabrication operations (installation of an additional fabrication station), and implementation of this method may raise difficulties in selecting suitable chemical agents (suitable composition of the lacquer for polarizing coating, solvent to remove the protective lacquer, etc.).
Technology has been developed which allows avoiding installation of special fabrication processes for producing polarizing films, obtained from organic dyes, with various configurations [Staral et al., U.S. Pat. No. 5,693,446]. This technology is based on using pre-fabricated polarizing films on a base, the so-called donors. This technology involves the known methods of mass transfer as a result of localized heating of the coating areas to be transferred [Chou et al., U.S. Pat. No. 5,506,189]. Heating may be implemented via thermal elements, and laser radiation, etc. This method allows obtaining polarizing coating of an arbitrary shape with high resolution of the pattern.
Difficulties arising in implementation of this method are related firstly to the structure of the transferring polarizing coating and the possible degradation of optical characteristics of the coating when it is locally heated up to the temperature necessary to carry out the transfer. Polarizing coating is obtained from lyotropic liquid crystal (LLC) dyes, molecules of which aggregate into supramolecular complexes. After application of LLC onto the substrate and inflicting the external shearing force supramolecular complexes become aligned in the direction of the influence. After the film dries (removal of the solvent), alignment of molecules is conserved. Therefore the crystalline order obtained from the lyotropic liquid crystal is conserved as well.
The anisotropy of optical, magnetic, or electric properties, the polarizing properties of the anisotropic crystal film is related to the crystalline order. The heating applied to the anisotropic crystal film potentially decreases the crystalline order, and thus the anisotropic properties are deteriorated as well. The risk to destroy the crystalline order with the heating could be substantially increased with particular material, increase of temperature, state of anisotropic crystal film, ambient conditions etc. Therefore the use of heating is generally undesirable for the technology.
Another possible solution is preliminary activation, i.e. preliminary influence onto the transferring areas of the film such as to weaken bonds between molecules or supramolecular complexes in the structure thereby providing the transfer of areas of the film from the donor plate to the receptor plate at significantly lower pressure. This does not result in degradation of anisotropy in the bulk material, and in the edges of the patterns.
Besides of general complexity, both heating and activation facilitated transfer technologies suffer from the roughness produced by the peel-off of the donor film performed after the transfer.
The peel-off stress comprises an expansion component and a shear component. Both components disturb the oriented molecules in the anisotropic crystal film. The disturbance comprises the deviation of the molecules' dipoles from the surface plane, thus producing the extensive distortion of the layer of the anisotropic crystal film material adhered to the surface. In particular, optical, magnetic, electrical, ferromagnetic and any other properties can be disturbed.
On the other hand, the production of the anisotropic crystal film with precisely pre-defined thickness is a complicated task when the film has to be produced directly from the solution of the polycyclic organic compound. Thus the thickness is adjusted using the multiple identical anisotropic crystal films with various thicknesses. This is possible since the order of the magnitude of anisotropic crystal film thickness can be varied in the extremely wide range from tenths nanometers to hundreds microns. It is desirable to remove all defects from the interface between films in order to obtain the homogenous film. It is desirable that the films' interfaces are reseated as well, because any traces of the interface boundary produce the interference effects and make worse optical properties. The peel-off disturbance described hereinbefore could substantially affect the properties of the multilayer film, additionally producing the interface effects.